1. Field of the Invention
The present invention relates to a laminated core used in a motor, a generator, a transformer, or the like, the laminated core being configured by laminating core members which are made of magnetic sheets. The invention relates also to a method and an apparatus for manufacturing a laminated core as well as a stator employing the laminated core.
2. Description of the Background Art
A conventional method of manufacturing a laminated core uses a punch swaging process in which core members are laminated as the same are punched from a beltlike thin sheet and swaged together. In the punch swaging process, thicknesswise protruding and recessed parts are formed in the individual core members with the protruding part formed on a front side of each core member and the recessed part formed in a rear side thereof, for example, and when a plurality of such core members are laminated, the core members are fixed one on top of another with the protruding and recessed parts of the core members adjoining in a laminating direction securely fitted and joined together by the application of pressure as described in Japanese Patent No. 3294348, for example.
Japanese Laid-open Patent Application No. 2003-324869 introduces another conventional method of laminating a plurality of core members by use of a dielectric adhesive. According to this method, the adhesive may be applied to surfaces of the individual core members by a steel sheet manufacturer or by a laminated core manufacturer (assembler) to join the core members. Alternatively, the laminated core manufacturer may by soak the stacked core members in a bath of the adhesive to join the core members together.
In addition, Japanese Patent No. 3822020 discloses an apparatus mounted on a press forming line for manufacturing a laminated core. The apparatus includes an adhesive applicator for applying adhesive at specific points in a spotted pattern on at least one of top and bottom surfaces of each thin-walled steel sheet (core member) and a holding mechanism in which individual core members punched into a specific shape by a pressing machine and applied with the adhesive are successively stacked and joined together by adhesive bonding.
There is a growing need today for energy savings and higher efficiency in various kinds of equipment using motors. In this connection, recent arguments have focused on drawbacks of the conventional manufacturing methods of laminated cores.
According to the aforementioned punch swaging process, the protruding and recessed parts are formed on both sides of each core member and the core members stacked one on top of another are swaged together by applying the pressure. This conventional method has a problem that the core members are deformed in areas around the protruding and recessed parts pressurized so that a dielectric coating formed on electromagnetic steel sheets could break, thereby causing short circuits between the laminated core members and resultant degradation of magnetic property of the laminated core. This problem has been a bottleneck in increasing the efficiency of the equipment using motors.
Although there is a known technique for reduce eddy current by laminating a larger number of thin-walled core members to improve the magnetic property, this approach poses a problem that it difficult to form the protruding and recessed parts on the thin-walled core members.
Also because swaged portions of the core members are joined simply by press-fitting the protruding parts into the recessed parts, not all of the laminated core members are perfectly fixed together but gaps may be created between some of the core members. Consequently, there has been a problem that the laminated core could produce noise when used due to relative movements of the core members.
One approach to reducing the degradation of the magnetic property of the laminated core due to processing deformation thereof would be to bond the stacked core members by an adhesive. This approach however causes a loss of cost and an environmental problem, because, in the manufacture of the laminated core, a steel sheet coated with a thermosetting resin adhesive at the steel sheet manufacturer is press-cut and unused part of the steel sheet trimmed away therefrom is discarded together with the adhesive coating.
When the laminated core manufacturer applies the adhesive as in the case of Japanese Patent No. 3822020, for example, there can occur sagging, clogging, webbing or like phenomena of the adhesive depending on the viscosity of the adhesive and/or cleanness of an applicator head, resulting in such problems as variations in spread of the adhesive and difficulties in achieving desired bonding and dimensional accuracies and bond strength. There can also occur such problems as dripping of the adhesive to manufacturing facilities or finished products (laminated cores) as well as difficulties in production line management and maintenance with respect to the shelf life of the adhesive and ambient temperature and humidity suitable for the prevention of adhesive clogging, webbing, and so on.
While the prior art discloses the method of laminating the stacked core members by soaking the same in the adhesive as shown in Japanese Laid-open Patent Application No. 2003-324869 as well as a method of causing the adhesive to infiltrate gaps between the cut-out core members, it is difficult for the adhesive to perpetrate into the gaps under atmospheric conditions. Thus, the stacked core members are often impregnated with the adhesive like varnish under vacuum pressure by a laborious process.
In the manufacture of a multi-block laminated core of a motor stator, a plurality of laminated core blocks produced by individually laminating core members, each having a tooth portion and a yoke portion, are arranged in an annular form and assembled together by shrink-fitting a frame on the laminated core blocks thus arranged. When a radial stress is exerted on the cylindrically arranged laminated core blocks from outside, as a result of shrinkage of the frame, a contact stress acts between the frame and the core blocks or between the core blocks. Part of the contact stress is left in the form of residual stress in the laminated core product at the end of this assembly process, and the residual stress within the laminated core could increase iron loss therein due to magnetic property degradation of core material of the laminated core especially in a high-efficiency motor. This has been a bottleneck in increasing the efficiency of the motor stator employing the multi-block laminated core.
In addition, parts of press-cut surfaces of the individual laminated core blocks constituting curved outer surfaces thereof are held in contact with the frame, so that the laminated core members, or laminations, made of electromagnetic steel sheets having insulating surface coatings are short-circuited each other through the frame. Other parts of the press-cut surfaces of the laminated core blocks constituting circumferential end surfaces thereof are short-circuited between the adjacent core blocks due to deviations of the thickness of the core material or gaps between the laminations. This also causes an increase in iron loss, serving as a hindrance to increasing the motor efficiency.